Loading Diagram

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philly

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I having been looking at a drawing that shows a loading diagram and have not exactly been able to figure out where all the numbers on the loading diagram come from.

I know that the numbers on each of he corners are the individual phase currents A, B, and C represented by T1, T2, and T3 respectively however I cannot seem to figure out what or how the numbers on the side of the triangle are derrived?

At first I was thinking that these were phase-phase currents however these seem to high, and because most of the loads are single phase I dont think these are any delta vs wye currents?

Can anyone tell me how these numbers on the triangle sides are calculated? I've tried adding and subtracting individual A,B, C line current but I cant seem to arrive at these numbers
 
I was not able to download the file. You may want to check it. It may be my internet connection.
 
the numbers on the side of the triangle represent the hypotenuse (square the two values on the two ends and take the square root of that)
 
nakulak said:
the numbers on the side of the triangle represent the hypotenuse (square the two values on the two ends and take the square root of that)
Click to expand...

I see mathmatically that the number on the side does appear to equal exactly as you said. I am having troublse seeing why. From a pure trigonomatry standpoint I dont see how the two values on the two ends could be used to calculate a "hypotenuse" since these two numbers dont appear to form a right triangle.

Electrically speaking I dont see why this would be either. I dont see two electrical phases that are 90deg out of phase with each other. I'm used to performing this calculation on a vector in the form R+jX however I dont see this relationship anywhere here. Can you explain further.

What would then this value on the side represent? The current between the two phases? That doesn't appear to make sense either.
 
Smart $ said:
It appears the one line shown on the drawing is only part of the entire loading on the switchgear. This missing part(s) could explain a lot :rolleyes:
Click to expand...

Good Point. I'll look for possible other parts to the drawing to see if it then makes sense.

Is this type of loading diagram typical for representing loading on these phase circuits? If so what to the sides usually represent?

Is there any reason why the sides of the triangle follow pythagoream's therom without any right angle relationship?
 
sorry I didn't note in my original post that I have no idea what is being represented (I just noticed the numerical relationship). If this is some sort of antique 2 phase where the phases are 90 degrees out, it may have some significance, but I didn't get the impression that was the case ? Post some more information, there are some guys here that will surely be able to explain this thing to you.
 
philly said:
Good Point. I'll look for possible other parts to the drawing to see if it then makes sense.
Click to expand...

A complete one line may help to determine why perhaps three of the numbers were used in the diagram, but I doubt it will explain the geometric dilusion :grin:

philly said:
Is this type of loading diagram typical for representing loading on these phase circuits? If so what to the sides usually represent?
Click to expand...

FWIW, I've never seen a geometric "loading diagram" on any "plan" drawing.

philly said:
Is there any reason why the sides of the triangle follow pythagoream's therom without any right angle relationship?
Click to expand...

I can't think of any :rolleyes:
 
drbond24 said:
Did you figure it out? Let us know; I'm very curious.
Click to expand...

When I questioned the engineer that designed this I got the following response:

"The numbers at the points of the triangle represent the phase currents (connected load to each phase). The numbers on the triangle sides represent the load currents. The diagram represents all the loads listed on the single line. One number is basically the other divided by the square root of three."

I am not buying this however. These are mostly single phase loads and these are all line currents. Because these are all line currents and L-L currents there is no delta/wye relationship that I can see that would cause the L-L current to be 1.73 times greater.

If one were a line current and the other were a load current inside a delta connected motor or transformer I could see this relationship, but I am not seeing it strictly dealing with line currents. I have questioned further.

Anyone agree?
 
philly said:
When I questioned the engineer that designed this I got the following response:

"The numbers at the points of the triangle represent the phase currents (connected load to each phase). The numbers on the triangle sides represent the load currents. The diagram represents all the loads listed on the single line. One number is basically the other divided by the square root of three."
Click to expand...

Tell your guy his calculator is broken. 978/1.73 = 564

Even if that explanation made sense, the math would be wrong. :)
 
philly said:
I having been looking at a drawing that shows a loading diagram and have not exactly been able to figure out where all the numbers on the loading diagram come from.

I know that the numbers on each of he corners are the individual phase currents A, B, and C represented by T1, T2, and T3 respectively however I cannot seem to figure out what or how the numbers on the side of the triangle are derrived?

At first I was thinking that these were phase-phase currents however these seem to high, and because most of the loads are single phase I dont think these are any delta vs wye currents?

Can anyone tell me how these numbers on the triangle sides are calculated? I've tried adding and subtracting individual A,B, C line current but I cant seem to arrive at these numbers
Click to expand...

I was too lazy to calculate it but it seems to me that it shows the phase-to-phase and phase-to-neutral load amperes. Don't know why because the rectifiers seem to be conencted to two phases. Maybe because they are not multiples of 3 and they wanted to know the unbalance?
 
philly said:
When I questioned the engineer...

...I am not buying this however...

...Anyone agree?
Click to expand...

I do not agree. Load currents add up vectorially. The attached pdf depicts the "FIELD" loads of the drawing you posted (the four on the left). Each brown, orange, and yellow vector represent the load current impressed upon the line to which it is connected They are all L-L loads, yet each load influences the line currents by both amount and phase angle.

View attachment 2639

(Note: The vectors depicted in the attached pdf assumes unity power factor loads. It is likely they are not. Therefore the representation is for an illustrative purpose only.)
 
Smart $ said:
I do not agree. Load currents add up vectorially. The attached pdf depicts the "FIELD" loads of the drawing you posted (the four on the left). Each brown, orange, and yellow vector represent the load current impressed upon the line to which it is connected They are all L-L loads, yet each load influences the line currents by both amount and phase angle.

View attachment 2639

(Note: The vectors depicted in the attached pdf assumes unity power factor loads. It is likely they are not. Therefore the representation is for an illustrative purpose only.)
Click to expand...

They are large rectifiers with lousy power factor AND high harmonic content.
 
weressl said:
They are large rectifiers with lousy power factor AND high harmonic content.
Click to expand...

A lagging power factor would change the vector angles by ?arccos (PF).

In the case of identical PF loads only, the result of adjusting each contributing vector would be the same as rotating the entire diagram by that amount of degrees.

AFAIK, harmonic currents do not affect the diagram.
 
Smart $ said:
I do not agree. Load currents add up vectorially. The attached pdf depicts the "FIELD" loads of the drawing you posted (the four on the left). Each brown, orange, and yellow vector represent the load current impressed upon the line to which it is connected They are all L-L loads, yet each load influences the line currents by both amount and phase angle.

View attachment 2639

(Note: The vectors depicted in the attached pdf assumes unity power factor loads. It is likely they are not. Therefore the representation is for an illustrative purpose only.)
Click to expand...

Thanks for the diagram. I am still waiting for the engineers answer.

I'm having trouble seeing where you are getting your angles for the load currents which you are adding vectorally to get the line current. I know all of the vectors are the L-L currents with their respective angles but I'm not seeing where you are getting the angles. Can you please explain? From looking at it, it appears that the L-L current angles are 30deg phase shifted from normal L-N currenat at 0,120,and 240?
 
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